Nothing will take the swelling away. It is caused by a release of gas due to a micro-short inside the cell. As Matt says, you can keep running them but they will be down on power and not as good as ones that haven't swollen.
If you run stock classes then get rid of them; you'll be down on speed and acceleration. If you run modified classes they'll work fine (just motor up to restore speed) and if they swell any more then retire them and dispose of them.
To retire them, fill a bucket with a salt-water solution, drop the cells in and leave them there for a fortnight until flat. Then take them to your local recycling centre and put them with the batteries pile.
There rest has been said - store at the right voltage (roughly 3.7 to 3.8v per cell) and cycle them once every six weeks or so back to that voltage. You know what happens if you store them fully charged...! HTH
